Simultaneous high-accuracy measurements of local heat transfer and phase distribution during convective condensation using non intrusive diagnostic tools

Abstract

An experimental setup was built to measure simultaneously the profiles of the phase distribution and the heat transfer coefficient in a minitube during convective condensation of HFE7000 at low mass velocities. The aim is to overcome the lack of measurements available in the literature in these conditions, mainly due to the difficulty to measure accurately heat transfer and phase distribution simultaneously. The metrology combines two high-precision measurement techniques allowing accurate measurement of the condenser wall temperature by infrared method and the thickness of the liquid film flowing inside the condenser by interferometric or confocal method. A specific protocol was developed to reduce the uncertainty on the wall temperature down to 0.08 °C. The flow regime varies from smooth annular to wavy annular with mean thickness of the liquid film less than 100 μm when the mass velocity is increased from 5 to 30 kg m−2 s−1. The heat transfer coefficient increases locally by up to 30% as the mass velocity increases. These profiles were than compared to the ones of both Nusselt theory and 5 correlations selected from the literature. None of them allow an accurate prediction of the heat transfer coefficient obtained experimentally.